The breath-to-breath variation of ventilation seen in active sleep in infants has a regular, oscillatory component. This oscillatory component can be detected by digital comb filtering, a technique we have applied to infants. We have shown that oscillations in breathing, when they become exaggerated, may result in what is clinically referred to as periodic breathing or apneic spells, and postulate that they may be related to the sudden infant death syndrome. We plan a series of experiments to test the following hypotheses: 1) that interventions, such as increasing lung volume or carbon dioxide breathing, that tend to prevent apnea will eliminate oscillatory breathing patterns, 2) that apneic spells due to passive obstruction of the airways and apneic spells due to decreased central ventilatory drive are both related to oscillatory breathing patterns and 3) that low hematocrit accentuates oscillatory breathing patterns. Ventilation will be monitored before and after the interventions described above. The ventilation signal will be passed through a set of digital comb filters, and the filtered signal compared to events in the unfiltered data as well as to magnetometer measurements of chest wall movement. In this manner the effect of the intervention on oscillatory breathing patterns and obstructive and central apnea can be assessed. These experiments may help elucidate the mechanism of apneic spells in infants and may provide a technique for predicting susceptibility to prolonged apnea.